title: High-protein, reduced-carbohydrate weight-loss diets promote metabolite profiles likely to be detrimental to colonic health.
abstract: BACKGROUND
  Diets that are high in protein but reduced in carbohydrate contents provide a common approach for achieving weight loss in obese humans. However, the effect of such diets on microbiota-derived metabolites that influence colonic health has not been established.
  
  
  OBJECTIVE
  We designed this study to assess the effect of diets with reduced carbohydrate and increased protein contents on metabolites considered to influence long-term colonic health, in particular the risk of colorectal disease.
  
  
  METHODS
  We provided 17 obese men with a defined weight-maintenance diet (85 g protein, 116 g fat, and 360 g carbohydrate/d) for 7 d followed by 4 wk each of a high-protein and moderate-carbohydrate (HPMC; 139 g protein, 82 g fat, and 181 g carbohydrate/d) diet and a high-protein and low-carbohydrate (HPLC; 137 g protein, 143 g fat, and 22 g carbohydrate/d) diet in a crossover design. Fecal samples were analyzed to determine concentrations of phenolic metabolites, short-chain fatty acids, and nitrogenous compounds of dietary and microbial origin.
  
  
  RESULTS
  Compared with the maintenance diet, the HPMC and HPLC diets resulted in increased proportions of branched-chain fatty acids and concentrations of phenylacetic acid and N-nitroso compounds. The HPLC diet also decreased the proportion of butyrate in fecal short-chain fatty acid concentrations, which was concomitant with a reduction in the Roseburia/Eubacterium rectale group of bacteria, and greatly reduced concentrations of fiber-derived, antioxidant phenolic acids such as ferulate and its derivatives.
  
  
  CONCLUSIONS
  After 4 wk, weight-loss diets that were high in protein but reduced in total carbohydrates and fiber resulted in a significant decrease in fecal cancer-protective metabolites and increased concentrations of hazardous metabolites. Long-term adherence to such diets may increase risk of colonic disease.
authors.affiliation: Rowett Institute of Nutrition and Health, University of Aberdeen, Aberdeen, United Kingdom.
authors.forename: Wendy R
authors.initials: WR
authors.lastname: Russell
authors.forename: Silvia W
authors.initials: SW
authors.lastname: Gratz
authors.forename: Sylvia H
authors.initials: SH
authors.lastname: Duncan
authors.forename: Grietje
authors.initials: G
authors.lastname: Holtrop
authors.forename: Jennifer
authors.initials: J
authors.lastname: Ince
authors.forename: Lorraine
authors.initials: L
authors.lastname: Scobbie
authors.forename: Garry
authors.initials: G
authors.lastname: Duncan
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Johnstone
authors.forename: Gerald E
authors.initials: GE
authors.lastname: Lobley
authors.forename: R John
authors.initials: RJ
authors.lastname: Wallace
authors.forename: Garry G
authors.initials: GG
authors.lastname: Duthie
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Flint
mesh_terms: D000328:Adult; D000368:Aged; D000975:Antioxidants / Q000032:analysis; D002273:Carcinogens / Q000032:analysis; D003108:Colonic Diseases / Q000453:epidemiology; D018592:Cross-Over Studies; D050528:Diet, Carbohydrate-Restricted / Q000009:adverse effects*; D004038:Diet, Reducing / Q000009:adverse effects*; D004043:Dietary Fiber / Q000008:administration & dosage / Q000378:metabolism; D004044:Dietary Proteins / Q000009:adverse effects* / Q000378:metabolism; D005051:Eubacterium / Q000254:growth & development / Q000302:isolation & purification; D005232:Fatty Acids, Volatile / Q000032:analysis / Q000737:chemistry; D005243:Feces / Q000737:chemistry / Q000382:microbiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009603:Nitroso Compounds / Q000032:analysis; D009765:Obesity / Q000150:complications / Q000178:diet therapy*; D010636:Phenols / Q000032:analysis; D010648:Phenylacetates / Q000032:analysis / Q000737:chemistry; D012306:Risk; D055815:Young Adult
chemical_list: D000975:Antioxidants; D002273:Carcinogens; D004043:Dietary Fiber; D004044:Dietary Proteins; D005232:Fatty Acids, Volatile; D009603:Nitroso Compounds; D010636:Phenols; D010648:Phenylacetates; C025136:phenylacetic acid